Beam extractor



Jan, 2(1), 1953 w. M. POWELL 2,626,351

BEAM EXTRACTOR Filed Aug. 17, 1948 5 Sheets-Sheet 1 /7 A90 3 20a [/70 /8 //60 g o .l U TRIGGER .L ISOLATING HIGH MANUAL TIMING TRIGGER VOLTAGE PULSE UNIT AMPLIFIER PULSE OPERATION GENERATOR CONTROL 30b Time (24 IZOMAC 22 23 HIGH 1 VOLTAGE w POWER SUPPLY INVENTOR. W/LJON M. POWELL flan/KM ATTORNEY 1 5 2 3, t w m 6, UV. v &m m w 2 m mw M M .m MP W m 5 %.W N Sm 1 A N a 0 w W w W H R 1.... E m NW W K W m d m M AM I m w m m, fl'i m I m m 3 1 5 9 7 1 l a. 2 m A w v d m w J w Jan, 26, 1953 w. M. POWELL BEAM EXTRACTOR 5 Sheets-Sheet 3 Filed Aug. 17, 1948 INVENTOR W/L so/v M POWELL ATTORNEY Jan. 26, 1953 w. M. POWELL 2,626,351

BEAM EXTRACTOR Filed Aug. 1'7, 1948 5 Sheets-Sheet 4 IN V EN TOR. W/LJO/V M. POWELL ,4 TTOR/VE Y Jan. 20, 1953 w. M. POWELL BEAM EXTRACTOR 5 Sheets-Sheet 5 Filed Aug. 17, 1948 INVENTOR. l/i/lLSO/V M; POWELL W/aam A TTORNEV Patented Jan. 20, 1953 BEAM EXTBACTO-R Wilson M. Powell, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application August 17, 1943, Serial No. 44,649

12 Claims.

This invention relates to a method and apparatus for the removal of a beam of charged particles from a particle accelerator such as a cyclotron. It is particularly concerned with the extraction of high velocity ions from a frequency modulated type of cyclotron by means of electrostatic defiecting electrodesv and magnetic-field neutralizing bars.

A detailed description of a conventional cyclotron will be found in U. S. Patent No. 1,948,334 granted to E. 0. Lawrence on February 20, 1934, entitled Method and Apparatus for the Acceleration of Ions. A means for withdrawing the ions from the magnetic field at a definite point in their circulatory paths has been described therein as consisting of a set of electrodes maintained at a suitable potential to draw the ions outwardly from the magnetic field. The ions are then drawn into a magnetic shield which serves to reduce the magnetic field intensity of the large magnetic poles sufficiently to allow the ions to deviate outwardly from the magnetic field by reason of their momentum. The above-mentioned ion accelerator employs a constant high frequency voltage for the acceleration of the ions in the magnetic field. As the orbits of the ions increase, the latter gradually get out of step with the radio frequency energy which is accelerating them, resulting finally in deceleration of the ions. Therefore, in such a type of ion accelerator, the accelerating voltage is made as high as possible in order that the maximum acceleration may be attained in the short time before the ions get out of phase with the accelerating force. The shorter accelerating time permits fewer orbits with relatively wide spacing or separation between sucoessive orbits. Such wide spacing has permitted the use of a deflector to which was continuously applied a high D. C. voltage. When orbitally traveling ions come within the influence of the charged deflector, they are electrostatically defiected outwardly into a magnetic shield which thereby allows the ions to travel out of the influence of the magnetic field.

The co-pending application No. 748,434 filed May 16, 1947, Patent No. 2,615,129, issued October 21, 1952, by Edwin M. McMillan for a Synchrocyclotron, makes use of a, rotating capacitor to suitably vary the accelerating R. F. voltage whereby the ions remain in phase with their accelerating force. In this type of ion. accelerator wherein the ions do not get out of step with the accelerating force, it is desirable that the ions travel as many orbits as possible in order that they may gain a maximum amount of kinetic energy.- This is accomplished by having the orbits of ion travel spaced as closely together as possible. Such closev spacing as is accomplished in a synchro-cyclotron prohibits the use of the D. C. type of electrostatic deflector utilized in older type cyclotrons. With the orbits so closely spaced, the D. C. electrostatic deflector affects not only the desired orbit but also several of the adjacent orbits, thus making it difficult to remove ions of uniform energy.

The present invention is an electrostatic deflector which ha a high voltage pulse applied to the deflector bars only when ions of a desired energy level are within the influence of the bars. This permitsthe withdrawal of ions at a maximum energy level without affecting any but the desired orbits.

The principalobject of the present invention is to provide a method and an apparatus for removing ions from an electromagnetic ion accelerator.

Another object of the present invention is to provide a method and an apparatus for removing ions from only the desired orbit in an ion accelerator such as a synchro-cyclotron.

Another object of this invention is to provide a pulsed deflector electrode which functions only when the accelerated ions have reached a desired energy level.

A furthr object of thisinvention is to provide a magnetic field neutralizing means whereby the high energy ions may be extracted from the magnetic field of the ion accelerator.

A still further object of this invention is 'to provide a deflector system which is effective to remove ions of any desired energy from an ion accelerator.

Other objects and advantages of the invention will become evident by reference to the following detailed description in conjunction with the accompanying drawings wherein:

Figure 1 is a simplified plan view showing the beam extractor and illustrating the theory of operation of the electrostatic deflector and magnetic shield thereof.

Fig. 2 is a one-line schematic diagram indicating the electrical components for the generation and formation of the pulses supplied to the electrostatic deflector.

Fig. 3 is a plan view partly diagrammatic of a cyclotroncomparable to a cross section on a horizontal plane taken between the poles of the magnet.

Fig. 4 is an enlargement of a portion of Fig. 3 showing; particularly thearticulation of the electrostatic-deflector and the means of apply- 3 ing the pulsed voltage to the electrostatic deflector bars.

Fig. 5 is a cross section taken on the vertical plane indicated by the line 5-5 of Fig. 4 and showing mechanical details of the pulse supply to the negative electrostatic deflector bars.

Fig. 6 is a cross section on a vertical plane indicated by the line 66 of Fig. 4 showing mechanical details of the pulse supply to the positive electrostatic deflector bars.

Fig. 7 is a vertical cross section taken on the plane indicated by the line l'! of Fig. 4 and showing the mechanical details of the linkage for adjusting the radius or" the electrostatic deflector bars.

Fig. 8 is a cross section on a horizontal plane, indicated by the line 88 of Fig. 9, showing the radial articulation of the magnetic shield.

Fig. 9 is a cross section on a vertical plane indicated by the line 9-9 of Fig. 8 showing the mechanical details of the mounting of the shield cars and the field correcting shims.

Reference is now made to Fig. l which shows diagrammatically a beam extractor indicated generally by an arrow B and which includes an electrostatic deflector I having negatively pulsed bars 2, positively pulsed bars 3, and a magnetic shield 5. Th electrostatic deflector i is curved to receive the flnal orbit of the accelerated particles indicated by a dashed line 4, and the particles are released from the deflector to travel a path indicated by a line of arrows I9 into the magnetic shield 9. Under the influence of a D electrode l2 and the magnetic field of magnetic poles (of which the lower pole l I only is shown), the accelerated particles start with a point 5 as their radial center. This point precesses in a circle of precession 6 until the particles enter the electrostatic deflector when their radial center is changed to a point 1 and, subsequently, to a point 8 upon leaving the static deflector I.

Referring to the block diagram of Fig. 2, a frequency modulated sine wave voltage is introduced through cable 39 to a manual pulse operation control i1 and to a trigger timing unit [8 through a current limiting resistor M. The output of unit it is fed to an isolating trigger amplifier IQ and then to a high voltage pulse generator 2 3. The latter is charged by a high voltage power supply 2! through a shielded cable [5, a charging inductance 22, and a. charging diode 23. unit has its own individual power supply fed from a common 120 volt A. C. line and insulated from the high voltage or charging diode 23 by a filament transformer 24. The theory of operation illustrated by Fig. l and the circuit for the formation of high voltage pulses Fig. 2 will be explained later in detail.

Reference is now made to Fig. 3 which illustrates a conventional frequency-modulated cyclotron utilizing my beam extractor, a pair of parallel D shaped electrodes [2, mounted in the magnetic field or a coaxial and spaced pair of magnet poles only the lower of which, H, is shown, are enclosed within an evacuated chamber 28. The D electrodes l2 are supported in the chamber 23 by a pair of combination bushings and conductors 30 of a transmission line 32 which has as its outer conductor a metallic housing 31 containing a high frequency oscillator 35, the latter being frequency modulated by a rotary condenser 33 connected in the oscillators transmission line 32. A variable-speed motor 34 drives the multi-bladed rotary condenser 33 at any desirable modulating frequency to compensate for the increasing orbits Each a of the accelerated particles. A loop 36 in the filament circuit and a loop 2'! in the plate circuit of the oscillator are adjacent to the transmission line conductors 36 thereby coupling the oscillator voltage to the D electrodes 12. A small loop 31 extending into the transmission line 32 and having a collar 38 with a concentric cable 39 fitted into the wall of the metallic housing 3| may be rotated so as to pick up any portion of the magnetic flux cutting across the area enclosed by the loop 3'1. The voltage thus induced is used as the triggering voltage applied to the pulsed are control unit I l and the trigger timing unit It of Fig. 2 for the electrostatic deflector l. An ion source 29 extending through a wall [3 of the evacuated chamber 28 releases ionized particles at the center of the magnet l l. A probe as protruding into the evacuated chamber 28 and slidably positioned by means of a probe extender 4| may be moved to intercept, and thereby sample, any orbit of the ionized particles during acceleration.

Attention is now directed to Figs. 4, 5, and 6 which show the structural elements of my improved beam extractor as utilized in the abovedescri'bed frequency modulated synchro-cyclotron. The electrostatic deflector I consists essentially of a pair of negatively pulsed bars 2 and a pair of positively pulsed bars 3 arranged in a parallel arc of 120 which is preferably symmetrical with respect to the particle source 29 near the edge of the magnet pole I l as best shown in Figs. 4, 5, and 6. A negative deflector bar support assembly 46 and a positive deflector bar support assembly 41 mounted on a horizontally movable base plate assembly 65 provide for the physical support of the bars 2 and 3 in space, their insulation from the base plate assembly 65, and the conduction of high voltage pulses from a high voltage pulse generator (Fig. 2). As noted in Fig. 3, flexible metallic strap 44 connected between the negative deflector bar support assembly 46 and a negative pulse conductor 62, and a flexible metallic strap connected between the positive deflector bar support assembly 41 and a positive pulse conductor 63 provide a flexible electrical connection from the conductors 62 and 63 to the electrostatic deflector l. The two electrical pulse conductors 62 and 63 pass out of the hermetically sealed cyclotron chamber 23 through the cyclotron tank wall 26 by means of combination bushings and seals 42 and 43.

A set of control screws 48, 49, and 50 mounted on the walls 25, 26, and I3 of the cyclotron tank housing 28 are connected to their respective mechanical linkages 5|, 52, and 53 which laterally position the electrostatic deflector movable base assembly 65.

The magnetic shield 9 (Figs. 8 and 9) consists of two slightly curved parallel iron bars mounted horizontally on a base plate I09 with One end inside the field of the magnet pole H and the other end of the magnetic shield 9 outside of the magnet pole ll. Two controls 54 and 55 (Fig. 3) mounted on the wall 26 of the cyclotron tank housing 28 and connected to their respective rotatable rods 58 and 59 rotate screws 56 and 5'! which laterally adjust the position of a magnetic shield base plate [09 on which the magnetic shield 9 is mounted. An exit tube 60 having an hermetioal aluminum foil seal BI is welded on the cyclotron tank wall 26 in line with the magnetic shield 9 so as to allow the beam of particles to leave the cyclotron tank 28 after passing through the magnetic shield 9.

Referring now to Fig. 4, the deflector bars 2 and 3 oi the electrostatic deflector assembly I are supported by several negativeand, positive deflector bar support assemblie 46 and 41 mountedon the movable base plate assembly 65 which is composed of articulated base plate sections 66, 6], 68, and 6-9; An articulating plate It, connecting base plate sections 66 and 61 with bolts I3, has milled slots 14 so as to permit free lateral movement of the base plate sections relative to each other. Base plate sections 67 and 68 arearticularly connected by an articulating plate 'II and a guide plate I6. Base plate 63 is hinged to the control screwmechanical linkage 52 which permits not only restricted articular motion but serves also to transfer the mechanical motion of the linkage 52 to the center base plate sections, as will be explained later. Control screw linkages 5| and 53 pivotally attached to base platesections 66 and 69* provide for the transfer of mechanical motion to the outer base plate sections. lhe sectionalized deflector-bars 2 and 3 attached to their respective deflector bar support assemblies 46 and l'l have sliding connectors 34 between her sections in order to maintain electrical contact between the bars during radial and configural adjustments.

Referring now to Fig, 5, the negative deflector bars 2 are supported by an upper support rod 87 and a lower supportrod 83 which are shaped so as to maintain a maximum clearance from the positive deflector bars 3 and are attached to a support fitting 86 on support cap 85; A porcelain insulator 84, bolted on the movable base plate section 67 bears and insulates from ground the support cap 85. Vertical adjustment supports 8| which slidably support the movable base plate assembly 65 are spaced at intervals under the movable base plate assembly and are pivotally bolted to the lower magnet pole II with a tilt adjusting bolt 83 on one end so as to vertically position the electrostatic deflector-in the plane of beam rotation.

In Fig. 6 the positively pulsed electrostatic deflector bars 3 are supported by straight and parallel upper and lower support rods 89 and 90 of the positive deflector bar support assembly ll and are clamped in place by upper and lower rod support plates HI and 92. A porcelain insulator 94 bolted to the movable base plate assembly 65 rigidly supports a metallic cap 93 on which the rod support plates are mounted and on which the positive flexible connecting strap 45 is attached by means of a connection-extension 95. All but two of the positive and negative deflector bar support assemblies 41 and 46 which areseparately and laterally spaced along the movable base plate assembly 65 (Fig. l) are for support only. The remaining centrally disposed two support assemblies serve also to apply the deflecting pulse from the high voltage pulse conductors 62 and 63 through flexible connecting straps 44 and 45 to their respective deflectorbar support assemblies.

Referring now to Fig. '7, there are shown the operational details of the mechanical linkage controlling the movement of the center base plate sections of the electrostatic deflector. An articulating plate 'II (Fig. 4) which is rigidly bolted to movable base platesection 61 and pivotallybolted to movable base plate section 68 by means of a guide bolt I5 articulately joins the two center base plate sections. The electrostatic deflector control linkage 52, pivotally bolted to a corner of base plate section 68 by means of a'pi'vot linkage bolt it, serves to impart mechanical motion to base plate section 68. The guide bolt 15 has an elongated; roundshank I00 adapted to slide along a guide plate 'slot 1-7 of a guide plate I6- which is rigidly boltedto the lower magnet pole I I-thereby insuring that both center base plate sections 57 and 68 will move radially wit-hanequal and linear motion. A long connecting rod I02 (Fig. 3) coupled between the radial adjustmentcontrol screw 49- (Fig. 3) and the adjusting linkage 52 bymeans of levers 91 and 99 attachedto a pivot 98 mounted on a square U type yoke IIII and bolted to the cyclotron tank wall 26, serves totransmit radial adjustments from; the manual control screw to the center base plate sections.

The following description of the mechanical details of the structure of the magnetic shield is made with reference to Fig-s. 8 and9. Rods I05 and IE6, which are connected to position adjusting screws 5'I-and 56 (Fig. 3), terminate in pivotal connections I01 and IOBattached to the lower magnetic deflector base plate IIlBand are adapted to move between lateral motionrestraining guides I It and I I I so as to position the magnetic shield with respect to the final radial center of orbitally accelerated particles. The backing plate II5, upon which is mounted the entire magnetic shield Q, is sustained by an upper base plate H2 and a lower base plate I69, both of which are strengthened by reinforcing plates H3 that serve to prevent the powerful field of the magnetic field of poles II and H5 from distorting or moving the shield. A group of shield-bar supports IIB and shield-bar support shims I20 rigidly bolt and laterally position, with respect to the backing plate H5, a pair of magnetic shield bars H3 and H9. Magnetic shims I2I, supported by shim supports I I? and laterally spaced by shim spacers I22, are used to adjust the magnetic flux field in which shield bars H8 and H9 areto function. Auxiliary field adjusting shims I23, attached to the magnetic shims I2I by brace plates I24 and shimmed by brace plate shims I25, have reinforcing members I26 bolted to the brace plates I24 for rigidity. The auxiliary field shims I23, which are used for minor flux field adjustments, have coil springs I21 mounted on spring supporting rods I28 bolted between the brace plates I24. The free end of the springs I21 bear against spring push-plates I29 bolted to the auxiliary field shims I23 thereby normally urging the auxiliary field shims into a nearly horizontal position (as shown by the dotted lines of Fig. 9) to facilitate removal of the magnetic shield assembly 9. When the magnetic field is on, however, the magnetic force of the poles- I I and I I4 is sufiicient to overcome the spring force of the coil springs I21, and the auxiliary shims I23 maintain a vertical position.

Considering now the operation of the beam deflector in a particular particle accelerator, such as the 184 inch cyclotron, ionized molecular particles such as positively charged hydrogen ions (protons), deuterons, or alpha particles (positively charged helium ions) are released from the source 2t (Fig. 3). When released, these particles are at position 5 in the cyclotron (Fig. 1), but under'the influence of the D electrode I2 and a'perpendicular magnetic field due to poles I I and H4 (Fig. 9), the particles leave the center 5 and commence to spiral around the circle of precession 6. The characteristics of cyclotron acceleration are such'that, as the particles revolve at high speed, the locus-of'centers of rotation form a small circle 6, inthis'case about two inches in diameter, which 'is known as the; circle of precession; The radial center performs one complete precession for about every twenty orbital revolutions of the particles. The particles are formed into groups or bunches spaced twenty revolutions apart by pulsing the source 29 (Fig. 3) only once for each precession. As the particles revolve, a sinusoidal decrease of frequency of the high frequency voltage on the D electrode I2 allows the particles to spiral outwardly from the center 5 yet remaining in step with the accelerating voltage. The particles thus spiral outwardly in bunches spaced twenty revolutions apart until the beam enters the electrostatic deflector I at which time the radius of revolution is about 81 inches. The deflector voltage is not applied until the radial center has precessed to about position 5 (Fig. 1) in order to obtain the optimum radial position. As the charged particles spiral into the deflector I, a 200 kv. pulse which rises from ten percent to ninety percent of full voltage in 0.1 microsecond is applied to the deflector bars 2 and 3 causing the outer pair of bars 3 to become positive and the inner pair of bars 2 to become negative. The polarity of the deflecting pulse is such that it tends to push the outward spiraling particles back toward the source, constraining them to follow the curvature of the deflector I. Since the deflectors radius of curvature is three inches less than the radius of curvature of the particles before entering the deflector, the radial center of the particles while in the deflector is shifted to point 7. The pulse which is applied just before the particles enter the deflector and removed just before the particles leave the deflector gives the ion particles a strong radial motion which is immediately opposed by the stability characteristics of the ions so that upon leaving the deflector field the ion particles tend to resume their orig inal radius of curvature. Due to the angular change of position of the particles, however, the radial center I extends three inches to the point 8 which is along a line composed of the exit of the deflector I and the restrained radial center I. The beam of ions now swings about point 8 as a center and moves along path I and out of the cyclotron field into the magnetic shield 9 which, by reducing the magnetic field in the path of the particles, guides the particles out of the cyclotron.

The ion particles which are generated in groups or bunches are separated sufficiently such that operation of the deflector influences but one group at a time. The deflector is operated only when the precession center is at position in order to take advantage of the decreased distance of the radial center to the entrance of the electrostatic deflector. If the deflector were operated with the precession center opposite position 5, approximately two inches would be lost, and the ion particles might strike or entirely miss the magnetic shield 9.

Referring to Figs. 5 and 6, the outer bars 3 are pulsed positively and the inner bars 2 are pulsed negatively. As the positively charged ion particles travel along the length of the electrostatic deflector I, they are repelled by the positive bars 3 and attracted by the negative bars 2 thus urging the particles inwardly toward the center. The deflector would also operate successfully if a pusher" charge were used in the deflector bars 2 and 3. That is, if the inner members 2 were made positive and the outer members 3 were made negative during the pulse, the beam would be forced outwardly instead of inwardly. This method has the disadvantage of subtracting the radius of the precession circle 6 from the final radius of curvature so that if the precession of the beam were sufliciently large, the beam might not get out at all. The maximum amount of deflection of accelerated particles is obtained with a deflector having an arc of 180. A deflector of less than 180 will not fully utilize the maximum possible outward shift of the radial center 7, whereas a deflector of more than 180 curvature will actually cause a recession of the radial center 1. In the present 184 inch cyclotron, a deflector having a curvature of about 120 is used to obtain satisfactory deflection and yet avoid physical interference with the D electrode I2.

After the ions leave the deflector I with their new radial center 8, they have gained a distance away from the initial center 5 equal to the distance between points 5 and 8 or, as in the 184 inch cyclotron at the University of California, about 6 inches. This distance is adequate to bring the ions within the influence of the magnetic shield 9 thereby lowering the circumferential magnetic force of poles I I and I II sufficiently to permit the ions to leave the magnetic field without disturbing any succeeding ion orbits. The magnetic shield 9 lowers the field strength of the magnetic field to a value less than thirty percent of what the field would be without the shield. Shims I2I and I23 are placed directly in front of the magnetic shield 9 to compensate for the change wrought in the magnetic field by the shield, thus permitting a uniform flux density up to the shield so as not to distort the orbits of the undeflected ions.

In order to remove ions of various energy levels, the electrostatic deflector I and the magnetic shield 9 are adjustable laterally with respect to the center of the cyclotron 5. When it is desired to deflect particles of lower energy, controls 48, E9, and 50 are turned so as to move the deflector I toward the particle source. Controls 54 and 55 are also rotated so as to move the shield 9 inwardly. For ions of higher kinetic energy, the controls for the electrostatic deflector I and the magnetic shield 9 are rotated to adjust them outwardly, thus intercepting ions of a higher speed and larger radius.

Referring again to Fig. 2, the function of the triggering and pulsin network will be briefly described. A more complete disclosure of the circuits and operation will be found in the copending applications of Quentin A. Kerns, No. 12,356 filed March 1, 1948, Patent No. 2,500,756, and No. 18,927 filed April 5, 1948, Patent No. 2,517,676. A frequency modulated voltage 39a varying between 9.5 and 11.8 megacycles and modulated by a 100 cycle per second voltage, is conducted directly to the pulsed arc control unit I! and by means of the voltage limiting resistor I4 to the trigger timing unit I8. The pulsed arc control unit II generates a square-wave gate voltage I'Ia which is out of phase with the F. M. wave 39a thereby permitting operation of the source 29 (Fig. 3) only on the downard or acceleratin portion of the F. M. cycle. The deflector trigger timing unit I8 correlates the inputs of the square-wave gate Ila and the F. M. wave 3912 so as to generate a 300 volt deflector trigger pulse I8a of about 0.2 microsecond duration which is amplified by the trigger amplifier I9 to form a 500 to 1000 volt square-Wave trigger pulse I9a. The high voltage pulse generator 20, consisting of a bank of high voltage capacitors fired by thyratrons, is triggered by the amplified trigger pulse I9a and delivers a positive kv. pulse 29a which is applied to the outer deflector bar 3 and a negative 100 kv. pulse 20b which is applied to the inner deflector bar2 of the electrostatic deflector l. The defiected particles passing between the positive and negative deflector bars 3 and 2 are, in effect, influenced by a 200 lav. pulse, since the positive and negative 100 kv. pulses applied to the bars 3 and 2 add to zoo kv.

The voltage for the operation of the deflector pulse generator Eil is generated by the high voltage power supply 2i which is adjustable from zero to kv. The charging inductance 22, by means of the energy contained in'its magnetic field, is able to supply half of the energy required every time the high voltage pulse generator 253 operates. Thus, the power supply 2 i, in Charging its capacitors and the charging inductance 22, can supply twice the voltage for which it is set. The charging diode 23 prevents the double voltage of power supply 23 from leaking ofi until the high voltage pulse generator 29 is triggered. The shielded cable serves to prevent its high flux field from inducing spurious voltages in associated wiring due to the high discharge currents present during pulse operation. The filament insulating transformer 24 serves to provide the proper filament voltage current for the charging diode 23, yet preventing the high voltage of power supply 24 from arcing to the relatively low-voltage power source.

While I have described the salient features of this invention in detail with respect to one embodiment, it will, of course, be apparent that nu merous modifications may be made within the spirit and scope of this invention. I do not therefore desire to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

1. In a deflector for the removal of ionized particles from an electromagnetic type of ionized particle accelerator, a magnetic shield comprising a plurality of curved and spaced ferromagnetic bars arranged along the path of travel of said particles in the magnetic field of said accelerator to reduce the magnetic flux in the path of said particles, means for effectin lateral adjustment of said bars, and magnetic field correcting shims disposed above, below and in front of said bars to compensate for the magnetic field distortion due to the latter.

2. In a particle deflector for the removal of ionized particles from an electromagnetic particle accelerator of the cyclotron type, a magnetic shield for the reduction of a portion of the magnetic flux field of said accelerator comprising a plurality of spaced and substantially parallel ferromagnetic bars arranged near the outermost orbit in the plane of rotation of said particles to reduce the magnetic flux in the path of said particles, means for effecting lateral adjustment of said bars, and magnetic field correcting shims of magnetic material disposed above, below and in front of said bars to compensate for the magnetic field distortion due to said bars.

3. In an electromagnetic particle accelerator of the cyclotron type, an extractor for ionized particles comprising a plurality of electrostatically pulsed conductors disposed near the path of said particles to alter the radial center of said rotationally accelerated particles, and a magnetic shield disposed near the particle exit of said accelerator to guide said particles with the altered radial center out of the accelerator.

i. In electromagnetic particle accelerator of the cyclotron type for the spiral acceleration of charged particles, a particle deflector compris- I0 ing a plurality of parallel spaced non ma'gnetic conductors formed into an arc not exceeding arranged in the plane of rotation of said charged particles, a high-voltage pulsing means for applying a D. C. pulse of the same polarity as said charged particles to certain of said conductors and of opposite polarity to the remainder of said conductors to constrain said particles to follow the curvature or" said conductors and thereby shift the radial center of said particles, and a plurality of parallel ferromagnetic bars arranged in the plane of rotation of said charged particles to lower the magnetic force in the path of said particles and positioned so as to receive those particles with said shifted radial center, thereby uiding said particles out of the particle accelerator.

5. In an electromagnetic particle accelerator or" the cyclotron type for the spiral acceleration of charged particles, a particle deflector comprising a plurality of non-magnetic segmented conductors disposed in parallel spaced relationship and formed into an are not exceeding 180 arranged in the plane of rotation of said charged particles, articulating means between said segmented conductors, means for adjusting the radius and the lateral position of said segmented conductors, high-voltage pulsing means for applying a D. 0. pulse of the same polarity as that of said charged particles to certain of said conductors and of opposite polarity to the remainder of said conductors to constrain said particles to follow the curvature of said conductors thereby shifting their radial center, a plurality of parallel ferromagnetic bars arranged in the plane of rotation and at the outermost orbit of said charged particles to weaken the magnetic field and guide said charged particles out of said particle accelerator, means for laterally adjusting said bars, and magnetic field correcting shims disposed above, below and in front of said bars to compensate for the magnetic field distortion due to the later.

6. In an electromagnetic particle accelerator for the spiral acceleration of ionized particles, a particle deflector comprising a plurality of arcuately shaped, adjustably spaced, conductive deflecting bars disposable along an outer orbit of said ionized particles, electrostatic pulsing means connected to said bars for altering the radial center of said particles during the interval that said particles are in said outermost orbit, and means for adjusting the position of said deflecting bars relative to any selected particle orbit.

7. In an electromagnetic type of particle accelerator having a particle deflector for the removal of ionized particles therefrom, an adjustable magnetic shield comprising a plurality of arcuately shaped ferromagnetic rods arranged along the exit path of said particles to reduce the intensity of magnetic flux in the path of said particles, lateral rod positioning means for efiecting adjustment of the position of said rods, and magnetic field correcting shims disposed above, below, and in front of said rods to compensate for the magnetic field distortion due to the latter.

8. In a particle deflector for the removal of positively charged particles from an electromagnetic particle accelerator of the cyclotron type, a magnetic shield for the reduction of a portion of the magnetic flux field of said accelerator comprising a pair of arcuately shaped, ferromagnetic bars horizontally disposed side by side in spaced relationship along an outer orbit in the orbit plane of said particles, field correcting shims above and below said bars, auxiliary field correcting shims above and below and in front of said bars, said auxiliary shims being held in correct vertical alignment by the magnetic field of said accelerator, and means for effecting lateral adjustment of said bars, shims, and auxiliary shims whereby the same may be positioned to provide maximum neutralization of the magnetic field of the particle accelerator in the path of the extracted particles.

9. In an electromagnetic particle accelerator of the cyclotron type, an extractor for ionized particles comprising a support mounted in the magnetic field of said accelerator and laterally adjustable in a plane which is normal to said field, a plurality of spaced electrical conductors mounted in insulated relation upon said adjustable support, said conductors having similar curvature and coinciding with a portion of an outer orbit of said particles, high voltage electrostatic pulsing means connected to said conductors for energizing the latter and deflecting said particles, and an adjustable magnetic shield disposed near the particle exit of said accelerator whereby particles deflected by said pulsed conductors are guided out of said accelerator by said magnetic shield.

10. In an electromagnetic particle accelerator of the cyclotron type, an extractor for ionized particles comprising a first laterally adjustable support mounted in the magnetic field of said accelerator, a plurality of parallel electrical conductors mounted in insulated relation on said adjustable support, said conductors extending arcuately for less than 180 of an outer orbit of said particles and coinciding with said outer orbit, high voltage electrostatic pulsing means connected to said conductors for deflecting said particles, a second laterally adjustable support mounted in the magnetic field of said accelerator, and a magnetic shield consisting of a pair of substantially parallel ferromagnetic bars attached to said second adjustable support and disposed near the particle exit of said accelerator for guiding said accelerated particles out of said accelerator upon energization of said conductors.

11. In a frequency-modulated cyclotron having a spaced pair of magnet poles, a pair of D shaped electrodes therebetween and a surrounding evacuated chamber, and a frequency-modulated oscillator coupled through a transmission line to said D shaped electrodes, the combination comprising a particle deflector having a plurality of arcuately shaped, adjustably spaced, conductive deflecting bars disposable along an outer orbit of particles accelerated by said cyclotron, electrostatic pulsing means connected to said bars for altering the radial center of said particles during the interval that said particles are in said outer orbit, and a coupling loop connected to said pulsing means and adjacent said transmission line for triggering said means.

12. The combination of elements set forth in claim 11 wherein said transmission line includes a pair of insulated conductors supporting said D shaped electrodes and a surrounding metallic housing, and said coupling loop is rotatable to vary the flux cutting thereacross.

WILSON M. POWELL.

REFERENCES CITED The following references are of record in the 30 file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Electronics, March 1947, F. M. Cyclotron, page 119.

General Electric Review, June 1947, Atomic Artillery by James Stokley, pages 9 through 19. 

